The invention relates generally to a system for the separation of gaseous mixtures containing essentially hydrogen (H.sub.2), methane (CH.sub.4) and carbon monoxide (CO) especially purified CO. Such a system generally comprises a physical low-temperature scrubbing step employing liquid methane as the scrubbing agent, as well as a downstream stripping and/or expansion step to separate H.sub.2 from the loaded methane, and thereafter a regeneration step to separate the loaded methane into enriched CO and CH.sub.4 fractions.
In a conventional process of this type ("Linde Reports on Science and Technology" No. 38, 1984, pages 37-47), carbon monoxide is scrubbed out at a low temperature in a scrubbing column by means of liquid methane from a crude gas, such as, for example, steam reformer gas, and H.sub.2 is withdrawn overhead from the scrubbing column. In order to obtain carbon monoxide as produce, CO is separated from methane in a regeneration column, for example by rectification, and the thus-purified CH.sub.4 is recycled into the scrubbing column. However, since a product CO of maximum purity is desired, the H.sub.2 content is reduced in a further process step, provided upstream of the regeneration, wherein the loaded methane from the scrubbing column is expanded and introduced into a stripping column. In this step, hydrogen, still contaminated with 20-60 mol-% of CO and 0.5-5 mol-% of CH.sub.4 is released. As contrasted with a mere expansion in an expansion tank, the stripping column is provided with heating means to evolve the contaminated hydrogen.
The proportion of CO remaining in the hydrogen represents, with regard to the yield of product CO, a loss of up to 10%, which has an adverse effect on the economy of the process. Typical yields of CO in the known process range from 94 to 97%.
Accordingly, in the conventional process, the yield of product CO is less than desired.